1. Field of Invention
The present invention relates to control systems for recovery of refrigerant from air conditioning systems.
2. Description of Prior Art
Fluorocarbons have been widely used as the refrigerant in chiller units for air conditioning, or HVAC, systems. Some of the most widely used fluorocarbons have been types of chlorinated fluorocarbon (CFC) sold under the trademark FREON.RTM.. In recent years, environmental concerns have arisen about fluorocarbon or CFC refrigerants and their possible harmful effects on the earth's atmosphere. Although until recently only disfavored for environmental reasons, it has now become unlawful to purposefully vent chlorinated fluorocarbon refrigerants to the atmosphere. For this and other reasons, the cost of such refrigerants has increased significantly. Although accidental leakage from system failures or breakdowns is not unlawful, it has become a very expensive and undesirable situation.
Generally, existing HVAC units have a graphite rupture disk on a centrifugal chiller unit as a portion of the original equipment. The disk has been designed to rupture when the system refrigerant pressure reached a specified excess pressure limit, typically 15 psig or so. In the past, refrigerant which escaped in the event of disk rupture was vented into the atmosphere.
Certain types of systems are available which attempt to limit or reduce the venting of refrigerant. These systems use a relief valve which opens at the excess pressure limit and closes again at a certain fraction or percentage (such as two-thirds) of the pressure limit. However, these systems allow repeated cycles of opening the relief valve, to vent refrigerant at the excess pressure limit, with subsequent closing of the relief valve. Eventually, unless the excess pressure problem was corrected, the entire charge of refrigerant could be vented in increments to the atmosphere.